1. Field of the Invention
The present invention relates to a mixer, and more particularly, to a mixer for converting a single signal into a differential signal in microwave and millimeter-wave transceiver structures, a transmitter and receiver having the mixer.
This work was partly supported by the IT R&D program of MIC/IITA [2005-S-046-03, Development of the basic spectrum resource utilizing technology].
2. Description of the Related Art
In the knowledge and information age, a wireless communications system has reached a stage in which a transmission rate of gigabits is required, and this results in the development of applications such as a wireless personal area network (WPAN) using millimeter-wave bands instead of existing frequency bands that have reached a saturated state. However, since a communications system using the millimeter-wave bands is constructed with individual devices, the communications system is large and expensive, and this causes a difficulty of generally utilizing the bands. In order to overcome the difficulty, millimeter-wave transceivers having a single chip type manufactured by using silicon (Si), germanium (Ge), or Si complementary metal-oxide-semiconductor (CMOS) technologies have been developed.
As a structure of the conventional transceiver, various structures such as a superheterodyne structure and a direct conversion structure have been proposed. In the structures, local oscillator (LO) frequencies input to mixers of a transmitter and a receiver are the same. It means that a fact that the transmitter and the receiver have different characteristics for LO and LO/2 frequencies is not utilized.
In addition, in order to output an intermediate frequency (IF) differential signal, the LO of the mixer has to be a differential signal, and a radio frequency (RF) signal is input to a source of a transistor, so that large conversion losses occur.